provide determined dependency load order

[mightyaleksey]

For example:

/* A.css */
.a {
  composes: a from './C.css';
}

.b {
  composes: b from './B.css';
  composes: b from './C.css';
}

should put deps in the order: B.css, C.css, A.css.

Also should warn about unclear order.

[mightyaleksey]

Presumably should be solved at css-modules/postcss-modules-extract-imports#131